If you have been staring at the screen for more than about 5 minutes:
Method One:
Do Something!! What you do may not be the "right" thing in terms of solving the problem, it typically wont, but it will start you moving and thinking. I have frequently heard people say to themselves "Well that was dumb, but maybe if I ..."
Although the method seems to work for most people, I can not personally attest to its rate of success since I have never had the problem
Method Two:
Beat your head against something hard until it stops hurting. At this point either the answer will come or you will achieve true enlightenment.
Mark